Hydraulic cylinders are used to affect movement of various machine components, for example to affect movement of a linkage member or a work tool relative to a machine frame. A hydraulic cylinder includes a piston positioned within a tube to define a rod-end and a head-end chamber therein. Selectively supplying high-pressure fluid to one of the rod-end and head-end chambers, while selectively communicating the other chamber with a low-pressure reservoir, affects relative movement of the piston within the tube and, thus, movement of the linkage member or work tool.
Often, two or more hydraulic cylinders are used in tandem to affect substantially the same relative movement between two components. For example, two hydraulic cylinders are commonly interconnected between a boom member or a blade of an earth-moving machine and the machine frame to simultaneously affect lifting of the boom member or tilting of the blade. During extension or retraction of the two hydraulic cylinders, one of the hydraulic cylinders can reach an end-of-stroke position (i.e., bottom out) before the other hydraulic cylinder. And, because both hydraulic cylinders receive pressurized fluid from a common source, the pressurized fluid supplied to the bottomed-out hydraulic cylinder, and the resulting pressure force acting on the piston of that hydraulic cylinder, can transfer a reactionary force to the boom member or blade, the machine frame, and/or the other hydraulic cylinder that can cause damage to the machine components.
One attempt to reduce the reactionary force described above is disclosed in U.S. Pat. No. 5,425,305 (the '305 patent) issued to Mauritz on Jun. 20, 1995. Specifically, the '305 patent describes a hydraulic piston disposed within a cylinder and having a bore therethrough that is spaced apart from and axially parallel to an axis of the piston. A tubular spool with closed ends and circular stops threadingly attached to each end is disposed within the bore, and has a length greater than the bore. The tubular spool has cross ports at each end that run perpendicularly to an axis of the spool. The cross ports are situated as close to the ends of the spool as possible. The cross ports intersect a hollow center of the spool and allow hydraulic oil to flow through the piston via the passage at the center of the spool when the valve is in an open position.
When working fluid is applied to a face of the piston of the '305 patent to move the piston, the working fluid forces the spool into the bore until one of the circular stops at the face of the piston abuts a seat and thereby stops fluid flow through the cross ports and the passage of the spool. As the piston approaches an end-of-stroke, the opposing circular stop engages an end cap of the cylinder and is urged together with the spool back through the bore of the piston to re-open the cross ports and the passage, thereby fluidly communicating opposing faces of the piston. By fluidly communicating the opposing faces of the piston, a buildup of pressure at the faces is reduced so as to reduce the reactionary force.
Although the spool-type relief valve of the '305 patent may help reduce the reactionary force of a hydraulic cylinder, it may be problematic. In particular, spool-type valves are known to have misalignment problems that can result in binding and damage of the spool. Further, spool-type valves are known to leak and have flow control difficulties. In addition, the valve of the '305 patent includes multiple separate internal parts that can reduce a durability of the valve while increase the costs thereof.
The disclosed hydraulic cylinder is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.